Composite sintering aid modified silicon nitride ceramic slurry, preparation method and application thereof

Abstract

The application belongs to the technical field of silicon nitride ceramics, and particularly relates to a composite sintering aid modified silicon nitride ceramic slurry, a preparation method and application thereof. The method comprises the following steps: dissolving lithium nitrate and magnesium nitrate in a solvent, adding ethyl silicate and citric acid, adjusting the pH to 3-4 and stirring to form a sol; dispersing silicon nitride powder in a silane coupling agent solution to obtain surface-modified silicon nitride powder, adding the surface-modified silicon nitride powder into the sol, and dispersing and stirring until gelation, and then drying to obtain modified silicon nitride powder coated with a Li2SiO3-MgO composite sintering aid, and then mixing the modified silicon nitride powder with photosensitive resin and a dispersing agent to obtain the composite sintering aid modified silicon nitride ceramic slurry. The uniform coating of the aid is realized through silane coupling agent modification and sol-gel coating, the problem of inconsistent local sintering in traditional mechanical mixing is avoided, and the sintering temperature during the preparation of the silicon nitride ceramic is effectively reduced by virtue of the composite aid system and the oxygen vacancy defect mechanism.

Description

Technical Field

[0001] This invention belongs to the field of silicon nitride ceramic technology, specifically relating to silicon nitride ceramic slurry modified with composite sintering aids, its preparation method, and its application. Background Technology

[0002] Silicon nitride ceramics, due to their high strength, high hardness, excellent high-temperature resistance, and corrosion resistance, have become ideal materials for fabricating complex high-end ceramic components and are widely used in aerospace, chemical, machinery, and integrated circuit fields. In recent years, the industry has developed various forming methods for manufacturing high-density, high-uniformity, and high-reliability silicon nitride ceramics, such as dry pressing, cold isostatic pressing, slip casting, tape casting, and injection molding. However, these traditional forming methods are difficult to manufacture ceramic products with complex structures and high precision. Furthermore, the aforementioned processing techniques are time-consuming and costly, which greatly limits the further development and application of silicon nitride ceramic materials. Therefore, there is an urgent need to develop a more efficient and economical method for preparing complex-shaped silicon nitride ceramics. Applying 3D printing technology to the manufacture of ceramic parts offers a new possibility for solving these problems and challenges. Among them, photopolymerization 3D printing technology, as an effective ultraviolet curing technology, has great potential in manufacturing high-precision, high-quality, complex-shaped ceramic parts. However, in photopolymer 3D printing of silicon nitride ceramics, insufficient curing depth and difficulty in sintering densification are two core bottlenecks restricting the quality and performance of the formed components. Using surface coating with composite sintering aids can address these issues simultaneously and specifically. On one hand, the strong scattering of ultraviolet curing light by silicon nitride ceramic powder is a key factor leading to insufficient curing depth. By coating the surface of silicon nitride powder with sintering aids possessing specific optical properties (such as low-refractive-index oxide aids), the overall refractive index of the powder can be effectively adjusted, reducing the difference between its refractive index and that of the organic photosensitive resin. This reduces the scattering loss of ultraviolet light in the slurry, improves the penetration depth and utilization rate of light energy, and thus improves the uniformity of the cured layer thickness, avoiding defects such as interlayer delamination. On the other hand, the covalent bond characteristics of silicon nitride itself result in low sintering activity. Traditional methods of directly mixing sintering aids are prone to problems such as uneven dispersion of aids and local imbalance of sintering rates. However, by surface coating treatment, sintering aids can form a uniform and dense coating layer on the surface of silicon nitride powder. This coating layer can diffuse and react with silicon nitride through a shorter path during sintering, thereby reducing the liquid phase generation temperature (without the need for extremely high sintering temperatures), promoting the densification of particles, and avoiding component segregation and internal porosity caused by aid agglomeration, thus significantly improving the density and mechanical properties of the final ceramic component. Therefore, developing a photopolymerization 3D printing silicon nitride slurry preparation method that can effectively improve the dispersibility of silicon nitride powder and enhance the curing performance of the slurry and the mechanical properties of the sintered components is of great significance for promoting the industrial application of silicon nitride ceramic 3D printing technology. Summary of the Invention To address the shortcomings of existing technologies, the present invention aims to provide a method for preparing silicon nitride ceramic slurry modified with composite sintering aids. By employing surface modification with silane coupling agents and sol-gel coating processes, uniform coating of composite sintering aids on the surface of silicon nitride powder is achieved, avoiding the problem of inconsistent local sintering caused by traditional mechanical mixing. Through the composite aid system and oxygen vacancy defect mechanism, the sintering temperature during the preparation of silicon nitride ceramics is effectively reduced.

[0003] Another object of the present invention is to provide a silicon nitride ceramic slurry modified with a composite sintering aid and its application.

[0004] The preparation method of the composite sintering aid modified silicon nitride ceramic slurry of the present invention includes the following steps: (1) Lithium nitrate and magnesium nitrate are mixed and dissolved in a solvent and stirred until completely dissolved to obtain a metal salt solution. Then, tetraethyl orthosilicate is added to the metal salt solution and stirred for 10-15 min to make the components initially mixed evenly. Then, citric acid is added, and the pH of the system is adjusted to 3-4 with 0.1 mol / L hydrochloric acid solution. The system is stirred at 40-50℃ for 30-40 min to form a sol. During this process, the metal ions and silicate esters undergo hydrolysis and condensation reactions. Citric acid plays a role in complexing and regulating the reaction process, promoting the formation of the sol. (2) Add silicon nitride powder to a silane coupling agent solution and ultrasonically disperse it for 30-60 min at 60-80℃ and 300-400W until it is uniformly dispersed. The organic groups at one end of the silane coupling agent molecule react chemically with the hydroxyl groups on the surface of the silicon nitride powder to form chemical bonds, while the organic groups at the other end face outwards, thereby changing the surface properties of the silicon nitride powder, reducing its surface energy, and improving its compatibility and affinity with the subsequent composite sintering aid sol. After the reaction is completed, collect the powder by centrifugation (5000-8000 r / min, 10-15 min) and wash it 3-5 times with anhydrous ethanol to remove unreacted silane coupling agent and other impurities. Finally, dry the washed powder in an oven at 80-120℃ for 4-6 h to obtain surface-modified silicon nitride powder. (3) Add the surface-modified silicon nitride powder to the sol and sonicate it at 300-400W for 30-40 minutes until it is evenly dispersed, so that the sol is evenly dispersed around the surface-modified silicon nitride powder. Then stir it at 50-60℃ at a stirring rate of 200-300r / min until it gels. During this process, the sol gradually transforms into a gel state, encapsulating the surface-modified silicon nitride powder. Place the gel product in an oven at 80-120℃ and dry it for 4-6 hours to remove the solvent, and obtain modified silicon nitride powder with Li2SiO3-MgO composite sintering aid on the surface. The surface coating layer contains oxygen vacancy defects, which can effectively reduce the ion diffusion activation energy during sintering and promote the sintering reaction. (4) The modified silicon nitride powder coated with Li2SiO3-MgO composite sintering aid is mixed evenly with photosensitive resin and dispersant to obtain composite sintering aid modified silicon nitride ceramic slurry.

[0005] In step (1), the mass ratio of lithium nitrate to magnesium nitrate is (3-5):1; the solvent is an ethanol-water mixture with a volume ratio of ethanol to water of 2:1; the mass-volume ratio of the total amount of lithium nitrate and magnesium nitrate to the solvent is 1:(3-5) g / mL; the volume ratio of tetraethyl orthosilicate to the solvent is 1:(5-8); and the amount of citric acid added is 0.5-1 wt.% of the total amount of lithium nitrate and magnesium nitrate.

[0006] In step (2), the particle size of silicon nitride powder is 0.5-5 μm; the silane coupling agent is KH560; the silane coupling agent solution is 5-10 wt.% silane coupling agent ethanol solution; and the mass ratio of silicon nitride powder to silane coupling agent solution is 1:(8-10).

[0007] In step (3), the mass ratio of surface-modified silicon nitride powder to sol is 1:(2-3).

[0008] In step (4), the amount of modified silicon nitride powder coated with Li2SiO3-MgO composite sintering aid added is 45-55% (v / v) of the total amount of modified silicon nitride powder coated with Li2SiO3-MgO composite sintering aid and photosensitive resin; wherein, the density of modified silicon nitride powder coated with Li2SiO3-MgO composite sintering aid is 3.2 g / cm³. 3 The density of the photosensitive resin is calculated to be 1 g / cm³. 3 calculate.

[0009] In step (4), the photosensitive resin is composed of oligomers, reactive diluents and photoinitiators in a mass ratio of (30-40):(70-60):3.

[0010] The oligomer is an epoxy acrylate or a polyurethane acrylate; the reactive diluent is one or more of 1,6-hexanediol diacrylate, 1,4-hexanediol diacrylate, tripropylene glycol diacrylate, hydroxyethyl acrylate, trimethylolpropane triacrylate, dipentaerythritol hexaacrylate, or pentaerythritol acrylate; the photoinitiator is one or more of 2,4,6-trimethylbenzoyl-diphenylphosphine oxide, ethyl 2,4,6-trimethylbenzoylphenylphosphonate, phenylbis(2,4,6-trimethylbenzoyl)phosphine oxide, or 2-phenylbenzyl-2-dimethylamine-1-(4-morpholinobenzylphenyl)butanone.

[0011] In step (4), the dispersant is one of PEG 200, BYK410, KOS110 or triethanolamine; the amount of dispersant added is 1-5 wt. of the modified silicon nitride powder with Li2SiO3-MgO composite sintering aid on the surface.

[0012] The composite sintering aid modified silicon nitride ceramic slurry is prepared using the above-mentioned preparation method for composite sintering aid modified silicon nitride ceramic slurry.

[0013] The application of the composite sintering aid modified silicon nitride ceramic slurry is used to prepare silicon nitride ceramics, which are formed by photopolymerization 3D printing, curing, and sintering.

[0014] Compared with the prior art, the beneficial effects of the present invention are as follows: (1) The preparation method of the composite sintering aid modified silicon nitride ceramic slurry of the present invention achieves uniform coating of composite sintering aid on the surface of silicon nitride powder by using silane coupling agent surface modification and sol-gel coating process, avoiding the problem of local sintering inconsistency in traditional mechanical mixing, and significantly improving the quality stability of ceramic products. (2) The method for preparing the composite sintering aid modified silicon nitride ceramic slurry of the present invention adopts a composite aid system (Li2SiO3 low melting point liquid phase + MgO controlled grain growth) and an oxygen vacancy defect activation mechanism, so that the sintering temperature of silicon nitride ceramics prepared by the slurry is reduced from the traditional 1800-1900℃ to 1650-1750℃, and it is compatible with ordinary atmosphere sintering furnaces, without the need for high vacuum equipment, further saving equipment and energy costs. Detailed Implementation

[0015] The present invention will be further described below with reference to the embodiments.

[0016] Unless otherwise specified, the raw materials used in the examples and comparative examples are all commercially available materials, and the process methods used in the examples and comparative examples are all conventional methods in the art.

[0017] The following is a description of some of the raw materials used in the examples and comparative examples: Bisphenol A epoxy acrylate, purchased from Shanghai Yinchang New Materials Co., Ltd. Polyurethane acrylate YC2188, purchased from Shanghai Yinchang New Materials Co., Ltd.; BYK410, purchased from BYK Chemicals, Germany; KOS110, purchased from Guangzhou Kangou Shuang Trading Co., Ltd.

[0018] Example 1 The preparation method of the composite sintering aid modified silicon nitride ceramic slurry includes the following steps: (1) Mix 3g of lithium nitrate and 1g of magnesium nitrate in 20mL of ethanol-water mixed solvent (13.3mL of ethanol and 6.7mL of water) and stir until completely dissolved to obtain a metal salt solution. Then add 4mL of tetraethyl orthosilicate to the metal salt solution and stir for 10min to make the components initially mixed evenly; then add 0.02g of citric acid and adjust the pH of the system to 3 with 0.1mol / L hydrochloric acid solution. Stir at 40℃ for 40min to form a sol. (2) 10g of silicon nitride powder (particle size 1±0.5μm) was added to 80g of KH560 ethanol solution with a concentration of 5wt.%, and ultrasonically dispersed at 60℃ and 400W for 30min until uniformly dispersed. Then, the powder was collected by centrifugation (5000r / min, time 15min), and washed 3 times with anhydrous ethanol. Finally, the washed powder was placed in an 80℃ oven and dried for 6h to obtain surface-modified silicon nitride powder. (3) Add 5g of surface-modified silicon nitride powder to 10g of sol, sonicate at 400W for 30min until uniformly dispersed, and then stir at 50℃ with a stirring rate of 300r / min until gelled. Place the gel product in an 80℃ oven and dry for 6h to obtain modified silicon nitride powder with Li2SiO3-MgO composite sintering aid on the surface; (4) Bisphenol A epoxy acrylate, 1,6-hexanediol diacrylate and 2,4,6-trimethylbenzoyl-diphenylphosphine oxide were mixed at a mass ratio of 35:65:3 and magnetically stirred for 2 hours at a speed of 500 r / min. Then, modified silicon nitride powder with surface coating of Li2SiO3-MgO composite sintering aid and KOS110 were added and stirred for another 2 hours. After homogenization for 5 minutes, the mixture was degassed to obtain the modified silicon nitride ceramic slurry with composite sintering aid. The amount of modified silicon nitride powder with surface coating of Li2SiO3-MgO composite sintering aid added was 50% (v / v) of the total amount of modified silicon nitride powder with surface coating of Li2SiO3-MgO composite sintering aid and photosensitive resin. The amount of dispersant added was 1 wt.% of modified silicon nitride powder with surface coating of Li2SiO3-MgO composite sintering aid.

[0019] The viscosity of the prepared composite sintering aid modified silicon nitride ceramic slurry was measured to be 3500 mPa·s.

[0020] 1g of the prepared composite sintering aid modified silicon nitride ceramic slurry was placed on the printing platform of the 3D printing equipment and irradiated with ultraviolet light with a wavelength of 405nm for 3s. The curing depth was measured to be 90μm.

[0021] Example 2 The preparation method of the composite sintering aid modified silicon nitride ceramic slurry includes the following steps: (1) Mix 5g of lithium nitrate and 1g of magnesium nitrate in 24mL of ethanol-water mixed solvent (16mL of ethanol and 8mL of water), and stir until completely dissolved to obtain a metal salt solution. Then add 3mL of tetraethyl orthosilicate to the metal salt solution and stir for 15min to make the components initially mixed evenly; then add 0.03g of citric acid, adjust the pH of the system to 4 with 0.1mol / L hydrochloric acid solution, and stir at 50℃ for 30min to form a sol; (2) 10g of silicon nitride powder (particle size 3±0.5μm) was added to 100g of KH560 ethanol solution with a concentration of 8wt.%, and ultrasonically dispersed at 70℃ and 350W for 45min until uniformly dispersed. Then, the powder was collected by centrifugation (6000r / min, time 12min), and washed 3 times with anhydrous ethanol. Finally, the washed powder was placed in an oven at 100℃ and dried for 5h to obtain surface-modified silicon nitride powder. (3) Add 5g of surface-modified silicon nitride powder to 12g of sol, sonicate at 300W for 40min until uniformly dispersed, and then stir at 60℃ with a stirring rate of 200r / min until gelled. Place the gel product in an oven at 120℃ and dry for 4h to obtain modified silicon nitride powder with Li2SiO3-MgO composite sintering aid on the surface; (4) Polyurethane acrylate YC2188, tripropylene glycol diacrylate and ethyl 2,4,6-trimethylbenzoylphenylphosphonate were mixed at a mass ratio of 35:65:3 and magnetically stirred for 2 hours at a speed of 500 r / min. Then, modified silicon nitride powder with surface coating of Li2SiO3-MgO composite sintering aid and BYK410 were added and stirred for another 2 hours. After homogenization for 5 minutes, the mixture was degassed to obtain the modified silicon nitride ceramic slurry with composite sintering aid. The amount of modified silicon nitride powder with surface coating of Li2SiO3-MgO composite sintering aid added was 50% (v / v) of the total amount of modified silicon nitride powder with surface coating of Li2SiO3-MgO composite sintering aid and photosensitive resin. The amount of dispersant added was 1 wt.% of modified silicon nitride powder with surface coating of Li2SiO3-MgO composite sintering aid.

[0022] The viscosity of the prepared composite sintering aid modified silicon nitride ceramic slurry was measured to be 2200 mPa·s.

[0023] 1g of the prepared composite sintering aid modified silicon nitride ceramic slurry was placed on the printing platform of the 3D printing equipment and irradiated with ultraviolet light with a wavelength of 405nm for 3s. The curing depth was measured to be 85μm.

[0024] Example 3 The preparation method of the composite sintering aid modified silicon nitride ceramic slurry includes the following steps: (1) Mix 4g of lithium nitrate and 1g of magnesium nitrate in 15mL of ethanol-water mixed solvent (10mL of ethanol and 5mL of water), and stir until completely dissolved to obtain a metal salt solution. Then add 3mL of tetraethyl orthosilicate to the metal salt solution and stir for 12min to make the components initially mixed evenly; then add 0.03g of citric acid, adjust the pH of the system to 3.5 with 0.1mol / L hydrochloric acid solution, and stir at 45℃ for 30min to form a sol; (2) 10g of silicon nitride powder (particle size 2±0.5μm) was added to 90g of KH560 ethanol solution with a concentration of 6wt.%, and ultrasonically dispersed at 80℃ and 300W for 30min until uniformly dispersed. Then, the powder was collected by centrifugation (7000r / min, time 10min), and washed 3 times with anhydrous ethanol. Finally, the washed powder was placed in an 80℃ oven and dried for 6h to obtain surface-modified silicon nitride powder. (3) Add 5g of surface-modified silicon nitride powder to 15g of sol, sonicate at 350W for 35min until uniformly dispersed, and then stir at 55℃ with a stirring rate of 350r / min until gelled. Place the gel product in a 100℃ oven and dry for 5h to obtain modified silicon nitride powder with Li2SiO3-MgO composite sintering aid on the surface; (4) Bisphenol A epoxy acrylate, trimethylolpropane triacrylate and phenyl bis(2,4,6-trimethylbenzoyl)phosphine oxide were mixed at a mass ratio of 35:65:3 and magnetically stirred for 2 hours at a speed of 500 r / min. Then, modified silicon nitride powder with surface coating of Li2SiO3-MgO composite sintering aid and KOS110 were added and stirred for another 2 hours. After homogenization for 5 minutes, the mixture was degassed to obtain the modified silicon nitride ceramic slurry with composite sintering aid. The amount of modified silicon nitride powder with surface coating of Li2SiO3-MgO composite sintering aid added was 50% (v / v) of the total amount of modified silicon nitride powder with surface coating of Li2SiO3-MgO composite sintering aid and photosensitive resin. The amount of dispersant added was 1 wt.% of modified silicon nitride powder with surface coating of Li2SiO3-MgO composite sintering aid.

[0025] The viscosity of the prepared composite sintering aid modified silicon nitride ceramic slurry was measured to be 3800 mPa·s.

[0026] 1g of the prepared composite sintering aid modified silicon nitride ceramic slurry was placed on the printing platform of the 3D printing equipment and irradiated with ultraviolet light with a wavelength of 405nm for 3s. The curing depth was measured to be 100μm.

[0027] Silicon nitride ceramic slurries modified with the composite sintering aids prepared in Examples 1-3 were used respectively to prepare silicon nitride ceramics by photopolymerization 3D printing and sintering. The preparation methods are as follows: 1) The silicon nitride ceramic slurry modified with composite sintering aid was added to the photopolymerization 3D printing equipment to print the green body. The printing wavelength was 405nm, the bottom layer was 3 layers, the bottom layer exposure time was 2000ms, the normal exposure time was 5000ms, and the layer thickness was 50μm. 2) Place the green body into a forced-air drying oven for drying at a temperature of 60℃ for 6 hours; 3) Place the dried green body in a tube furnace and heat it from room temperature to 400℃ at a heating rate of 1℃ / min under a nitrogen atmosphere. Hold the temperature for 120 min, then heat it to 1000℃ at a heating rate of 2℃ / min and hold it for 60 min. Finally, cool the sample to room temperature at a cooling rate of 2℃ / min to complete the degreasing of the silicon nitride ceramic green body.

[0028] 4) The degreased silicon nitride ceramic blank is placed in an atmosphere sintering furnace. Under a nitrogen atmosphere and a pressure of 3 MPa, the temperature is increased from room temperature to 1000℃ at a heating rate of 10℃ / min and held for 120 min. Then, the temperature is increased to 1650℃ at a heating rate of 2℃ / min and held for 120 min. Finally, the sample is cooled to room temperature at a cooling rate of 2℃ / min to obtain silicon nitride ceramic.

[0029] Comparative Example 1 The difference from Example 1 is that, in the preparation method of the composite sintering aid modified silicon nitride ceramic slurry, unmodified silicon nitride powder is used to replace the modified silicon nitride powder coated with Li2SiO3-MgO composite sintering aid in an equal amount.

[0030] The method for preparing the silicon nitride ceramic slurry includes the following steps: Bisphenol A epoxy acrylate, 1,6-hexanediol diacrylate, and 2,4,6-trimethylbenzoyl-diphenylphosphine oxide were mixed at a mass ratio of 35:65:3 and magnetically stirred at 500 r / min for 2 h. Then, silicon nitride powder (particle size 1 ± 0.5 μm) and KOS110 were added, and stirring was continued for 2 h. After homogenization for 5 min, the mixture was degassed to obtain the composite sintering aid modified silicon nitride ceramic slurry. The amount of silicon nitride powder added was 50% (v / v) of the total amount of silicon nitride powder and photosensitive resin, and the amount of dispersant added was 1 wt.% of silicon nitride powder.

[0031] The viscosity of the prepared composite sintering aid modified silicon nitride ceramic slurry was measured to be 3700 mPa·s.

[0032] 1g of the prepared composite sintering aid modified silicon nitride ceramic slurry was placed on the printing platform of a 3D printing equipment and irradiated with ultraviolet light at a wavelength of 405nm for 3s. It did not cure. This is because the refractive index and absorbance of silicon nitride powder are relatively large, which hinders the effective transmission and utilization of ultraviolet light in the slurry system, thus preventing curing.

[0033] Comparative Example 2 The difference from Example 1 is that, in the preparation method of the modified silicon nitride ceramic slurry with composite sintering aid, the modified silicon nitride powder coated with Li2SiO3-MgO composite sintering aid is replaced with unmodified silicon nitride powder, and the amount of silicon nitride powder added is 40% (v / v) of the total amount of silicon nitride powder and photosensitive resin.

[0034] The method for preparing the silicon nitride ceramic slurry includes the following steps: Bisphenol A epoxy acrylate, 1,6-hexanediol diacrylate, and 2,4,6-trimethylbenzoyl-diphenylphosphine oxide were mixed at a mass ratio of 65:35:5 and magnetically stirred at 500 r / min for 2 h. Then, silicon nitride powder (particle size 2±1 μm) and KOS110 were added, and stirring was continued for 2 h. After homogenization for 5 min, the mixture was degassed to obtain the composite sintering aid modified silicon nitride ceramic slurry. The amount of silicon nitride powder added was 40% (v / v) of the total amount of silicon nitride powder and photosensitive resin, and the amount of dispersant added was 1 wt.% of silicon nitride powder.

[0035] The viscosity of the prepared composite sintering aid modified silicon nitride ceramic slurry was measured to be 2000 mPa·s.

[0036] 1g of the prepared composite sintering aid modified silicon nitride ceramic slurry was placed on the printing platform of the 3D printing equipment and irradiated with ultraviolet light with a wavelength of 405nm for 3s. The curing depth was measured to be 60μm.

[0037] Silicon nitride ceramics were prepared by photopolymerization 3D printing and sintering using the silicon nitride ceramic slurry obtained in Comparative Example 2. The preparation method is as follows: 1) The silicon nitride ceramic slurry modified with composite sintering aid was added to the photopolymerization 3D printing equipment to print the green body. The printing wavelength was 405nm, the bottom layer was 3 layers, the bottom layer exposure time was 2000ms, the normal exposure time was 5000ms, and the layer thickness was 50μm. 2) Place the green body into a forced-air drying oven for drying at a temperature of 60℃ for 6 hours; 3) Place the dried green body in a tube furnace and heat it from room temperature to 400℃ at a heating rate of 1℃ / min under a nitrogen atmosphere. Hold the temperature for 120 min, then heat it to 1000℃ at a heating rate of 2℃ / min and hold it for 60 min. Finally, cool the sample to room temperature at a cooling rate of 2℃ / min to complete the degreasing of the silicon nitride ceramic green body.

[0038] 4) The degreased silicon nitride ceramic blank is placed in an atmosphere sintering furnace. Under a nitrogen atmosphere and a pressure of 3 MPa, the temperature is increased from room temperature to 1000℃ at a heating rate of 10℃ / min and held for 120 min. Then, the temperature is increased to 1800℃ at a heating rate of 2℃ / min and held for 120 min. Finally, the sample is cooled to room temperature at a cooling rate of 2℃ / min to obtain silicon nitride ceramic.

[0039] Referring to GB / T 6569-2006, the flexural strength (MPa) of silicon nitride ceramics prepared using silicon nitride ceramic slurries obtained in Examples 1-3 and Comparative Example 2 was tested, and the test results are shown in Table 1.

[0040] Table 1 Performance Test Results

[0041] As shown in Table 1, the silicon nitride ceramic prepared in Example 1 exhibits higher flexural strength. This is because smaller silicon nitride powder particle size results in a larger specific surface area and higher surface energy, making diffusion and densification easier to occur during sintering, thus leading to better mechanical properties of the silicon nitride ceramic. In contrast, the silicon nitride ceramic prepared in Comparative Example 2 exhibits lower flexural strength. This is due to the lower solid content and higher organic content in the slurry, leading to greater volatilization during drying and sintering, which easily results in a larger shrinkage rate of the green body. Simultaneously, the larger particle spacing necessitates a longer sintering time or higher temperature for densification, and may be accompanied by abnormal grain growth, thereby reducing strength.

Claims

1. The application of a composite sintering aid modified silicon nitride ceramic slurry, characterized in that, This material is used to prepare silicon nitride ceramics, which are formed by photopolymerization 3D printing, curing, and sintering. The preparation method of the composite sintering aid modified silicon nitride ceramic slurry includes the following steps: (1) Lithium nitrate and magnesium nitrate are mixed and dissolved in a solvent, tetraethyl orthosilicate is added, and after stirring evenly, citric acid is added. Then, the pH of the system is adjusted to 3-4 by hydrochloric acid solution and stirred to form a sol. (2) Add silicon nitride powder to a silane coupling agent solution and disperse evenly. After centrifugation, washing and drying, surface-modified silicon nitride powder is obtained. (3) Add the surface-modified silicon nitride powder to the sol, disperse it evenly, and continue stirring until gelation. After drying, the modified silicon nitride powder with Li2SiO3-MgO composite sintering aid is obtained. (4) The modified silicon nitride powder coated with Li2SiO3-MgO composite sintering aid is mixed evenly with photosensitive resin and dispersant to obtain composite sintering aid modified silicon nitride ceramic slurry. In step (4), the amount of modified silicon nitride powder coated with Li2SiO3-MgO composite sintering aid added is 45-55 vol% of the total amount of modified silicon nitride powder coated with Li2SiO3-MgO composite sintering aid and photosensitive resin. In step (4), the photosensitive resin is composed of oligomers, reactive diluents and photoinitiators in a mass ratio of (30-40):(70-60):3; The oligomer is an epoxy acrylate or a polyurethane acrylate; the reactive diluent is one or more of 1,6-hexanediol diacrylate, 1,4-hexanediol diacrylate, tripropylene glycol diacrylate, hydroxyethyl acrylate, trimethylolpropane triacrylate, dipentaerythritol hexaacrylate, or pentaerythritol acrylate; the photoinitiator is one or more of 2,4,6-trimethylbenzoyl-diphenylphosphine oxide, ethyl 2,4,6-trimethylbenzoylphenylphosphonate, phenylbis(2,4,6-trimethylbenzoyl)phosphine oxide, or 2-phenylbenzyl-2-dimethylamine-1-(4-morpholinobenzylphenyl)butanone; and the dispersant is one of PEG 200, BYK410, KOS110, or triethanolamine. The preparation method of the silicon nitride ceramic is as follows: 1) The silicon nitride ceramic slurry modified with composite sintering aid was added to the photopolymerization 3D printing equipment to print the green body. The printing wavelength was 405nm, the bottom layer was 3 layers, the bottom layer exposure time was 2000ms, the normal exposure time was 5000ms, and the layer thickness was 50μm. 2) Place the green body into a forced-air drying oven for drying at a temperature of 60℃ for 6 hours; 3) Place the dried green body in a tube furnace and heat it from room temperature to 400℃ at a heating rate of 1℃ / min under a nitrogen atmosphere. Hold it at this temperature for 120 min, then heat it to 1000℃ at a heating rate of 2℃ / min and hold it for 60 min. Finally, cool the sample to room temperature at a cooling rate of 2℃ / min to complete the degreasing of the silicon nitride ceramic green body. 4) The degreased silicon nitride ceramic blank is placed in an atmosphere sintering furnace. Under a nitrogen atmosphere and a pressure of 3 MPa, the temperature is increased from room temperature to 1000℃ at a heating rate of 10℃ / min and held for 120 min. Then, the temperature is increased to 1650℃ at a heating rate of 2℃ / min and held for 120 min. Finally, the sample is cooled to room temperature at a cooling rate of 2℃ / min to obtain silicon nitride ceramic.

2. The application of the composite sintering aid modified silicon nitride ceramic slurry according to claim 1, characterized in that, In step (1), the mass ratio of lithium nitrate to magnesium nitrate is (3-5):1; the solvent is an ethanol-water mixture; the mass-volume ratio of the total amount of lithium nitrate and magnesium nitrate to the solvent is 1:(3-5) g / mL; the volume ratio of tetraethyl orthosilicate to the solvent is 1:(5-8); and the amount of citric acid added is 0.5-1 wt.% of the total amount of lithium nitrate and magnesium nitrate.

3. The application of the composite sintering aid modified silicon nitride ceramic slurry according to claim 1, characterized in that, In step (2), the particle size of silicon nitride powder is 0.5-5 μm; the silane coupling agent is KH560; the silane coupling agent solution is 5-10 wt.% silane coupling agent ethanol solution; and the mass ratio of silicon nitride powder to silane coupling agent solution is 1:(8-10).

4. The application of the composite sintering aid modified silicon nitride ceramic slurry according to claim 1, characterized in that, In step (3), the mass ratio of surface-modified silicon nitride powder to sol is 1:(2-3).

5. The application of the composite sintering aid modified silicon nitride ceramic slurry according to claim 1, characterized in that, In step (4), the amount of dispersant added is 1-5 wt. of the modified silicon nitride powder with Li2SiO3-MgO composite sintering aid on the surface.

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